To prevent a user's (customer's) rejection of payment and non-recognition of an order, the technology for adding a user's digital signature to an order is used today in an electronic commerce on the Internet.
A private key stored, for example, in a smart card is used as a digital signature. However, using such a private key as a digital signature requires the user terminal to have a special unit such as a smart card reader.
Also, electronic commerce on the Internet is increasingly targeted not only at personal computers but also at cellular phones.